Tropospheric ozone change from 1980 to 2010 dominated by equatorward redistribution of emissions.

Abstract

Since 1980, anthropogenic emissions of ozone precursors have decreased in developed regions, but increased in developing regions, particularly East and South Asia, redistributing emissions equatorwards1–4. Modeling studies have shown that the tropospheric ozone burden (BO3) is much more sensitive to emission changes in the tropics and Southern Hemisphere (SH) than other regions5–9. However, the effect of the spatial redistribution of emissions has not been isolated. Here we use a global chemical transport model to consider changes in anthropogenic short-lived emissions from 1980 to 2010, and separate the influence of changes in the spatial distribution of emissions from the total emission increase, on BO3 and surface ozone. We estimate that the spatial distribution change increased BO3 by slightly more than the combined influences of changes in the global emission magnitude itself and in global methane. These results are explained by the strong convection, fast reaction rates, and strong NOx sensitivity in the tropics and subtropics. Emissions increases in Southeast, East, and South Asia may be most important for the BO3 change. The spatial distribution of emissions has a dominant effect on global tropospheric ozone, suggesting that the future ozone burden will be determined mainly by emissions from the tropics and subtropics.